1. Field of the Invention
The present invent;on relates to a process for recycling of waste streams, particularly petroleum waste streams, generated in refinery operations. More particularly, the present invention relates to a delayed coking process employing a feed stream produced from a petroleum waste stream.
2. Description of the Prior Art
Many refineries, chemical plants, waste water treatment plants and other such industrial and municipal facilities generate waste products in the course of their operation. For example, in the refining of petroleum there are produced waste products or streams such as heavy oil sludges, biological sludges from waste water treatment plants, activated sludges, gravity separator bottoms, storage tank bottoms, oil emulsion solids including slop oil emulsion solids and dissolved air flotation (DAF) float from flocculation separation processes, etc. The disposal of these waste products can create difficult and expensive environmental problems primarily because the waste streams are not readily amenable to conversion to more valuable, useful or ecologically innocuous products.
Several methods have been proposed for dealing with the disposal, in an economical and environment;ally acceptable fashion, of waste products such as petroleum refinery sludges and other such waste products. In U.S. Pat. No. 3,917,564 (Meyers), incorporated herein for all purposes, there is a process disclosed in which sludges and other by-products of industrial and municipal activities are added to a delayed coker as an aqueous quench medium during the quench portion of the delayed coking cycle. The combustible solid portions of the by-product become a part of the coke, and the non-combustible solids are distributed throughout the mass of the coke so that the increase in the ash content of the coke is within commercial specifications, especially for fuel grade coke products.
Another proposal for dealing with petroleum sludges is disclosed in U.S. Pat. No. 4,666,585 (Figgins), incorporated herein for all purposes, which discloses a process in which petroleum sludges are recycled by adding them to the feedstock to a delayed coker before the quenching cycle so that the sludge, together with the feed, is subjected to delayed coking. This process has the desirable aspect of subjecting the combustible portion of the sludge to the high coking temperatures so that the conversion either to coke or the distillation of residual hydrocarbon products takes place. However, the presence of water in the sludge tends to lower the coking temperature unless compensation is made for this factor, for example, by increasing the operating temperature of the coking furnace, which in turn may decrease the yield of the more desirable liquid product from the delayed coking process. In addition, the amount of sludge that may be added to the coker feed is limited by the presence of the relatively large amount of water in the sludge. As described in the patent, the amount of sludge is limited to a maximum of 2 weight percent.
Yet another proposal for dealing with petroleum sludges is disclosed in U.S. Pat. No. 4,874,505 (Bartilucci), incorporated herein for all purposes, in which oily sludges and other refinery waste streams are segregated into a high oil content waste that is injected into a delayed coking unit during the coking phase of the cycle and a high water content waste that is injected during the quenching phase of the delayed coking cycle. This process purportedly increases the capacity of the delayed coker to process refinery wastes and sludges and has the potential for improving the quality of the resulting coke obtained from the process. Using this process, refinery sludges can be added at a rate of up to about 2 bbl/ton of coke produced.
U.S. Pat. No. 5,009,767 (Bartilucci, et al.), incorporated herein for all purposes, discloses a process similar to the earlier Bartilucci patent modified by the fact that the high oil content sludge is de-watered prior to being introduced into the delayed coking unit during the coking phase of the cycle.
While the above processes are effective to a certain degree in disposing of waste products such as refinery sludges, in general they suffer from the disadvantages such that, in general, there is a significant loss of valuable oil (organics), which is absorbed in the coke or collected in the blow-down system. Furthermore, with quench cycle injection of raw oil sludges, there is a tendency for oily build-up to occur in the coke drum, and the volatile combustible matter (VCM) levels in the coke are often objectionably high.